It is known to provide breakpointing mechanisms to assist in the analysis and debugging of data processing systems. With the advent of increasingly the complex data processing systems, and program code executing on such data processing systems, the provision of diagnostic/analytical mechanisms, such as breakpointing mechanisms and trace mechanisms, has becoming increasingly important to assist in the rapid and efficient development of hardware and software.
It is known to provide tracing mechanisms which output trace data indicative of a stream of data processing operations being performed. It is also known to provide breakpointing mechanisms which, when a breakpoint condition arises during program execution, trigger a breakpoint response.
One type of known breakpoint mechanism is to insert breakpoint instructions within the program flow. When these breakpoint instructions are encountered, they redirect processing to a breakpoint handler. The state of the system at that breakpoint can then be investigated and this information used for diagnostic/analytical purposes. A disadvantage with inserting breakpoint instructions is that they necessarily disturb the normal operation of the program code and it is difficult to select where to insert those breakpoint instructions to help analyse/diagnose a problem which may be arising. In program code that may be many thousands or tens of thousands of instructions in length, identifying the points at which it is appropriate to insert breakpoint instructions can be a difficult task.
Another known type of breakpointing mechanism relies upon identifying memory accesses with particular characteristics. The breakpointing mechanisms provided by the ARM7TDMI processor of ARM Limited, Cambridge, England include address and data watchpoints. Using these mechanisms, a breakpointing circuit can be programmed to trigger a breakpoint response when a memory access occurs to a memory address having a predetermined characteristic or to a data value with a predetermined characteristic. Whilst these breakpointing techniques are useful and flexible, they do not provide convenient mechanisms for triggering breakpoints in all circumstances where this might be useful. Not all points at which it may be desired to trigger a breakpoint involve a memory access having characteristics which can be used to trigger either an address watchpoint or a data watchpoint using the known mechanisms.